With the exception of blood, bone is the most frequently transplanted tissue in humans. With an aging population and with an increasing number of younger and more active patients undergoing, for example, hip replacement, revision surgery is often required. Currently, fresh frozen donor bone is the most effective graft material available for difficult clinical situations. Although bone transplantation has been used as the standard approach for reconstruction following excision of diseased bone, some problems remain unsolved. Among these, non-union fracture and loosening are major problems responsible for the failure of operations (especially for more extensive operations or after multiple operations), due to poor incorporation of allografts into host bone.
Bone formation in adult humans is a complex and closely regulated process. All bone is remodeled by the coordinated actions of bone resorbing (osteoclasts) and bone forming (osteoblasts) cells that are under the regulatory control of local cytokines generated in the environment of the remodeling cells. These local factors are comprised of peptides and nonpeptides. These factors are often incorporated into non-collagenous protein of bone matrix, released in an active form when bone is remodeled. Complex interactions between these factors and their target cells are responsible for the normal delicate balance between bone resorption and bone formation.
Unlike most other organ systems, the specific cellular components of bone only account for a minor portion of tissue weight. The major component of bone is matrix, which accounts for 90-95% of the tissue weight. Bone matrix includes mineral phases and protein phases, which are portioned 60-65% and 40-35%, respectively, of non-cellular bone weight. The non-collagenous proteins are heterogeneous in origin and some appear to be produced by bone cells while others are incorporated from or are concentrated from serum. The non-collagenous proteins are laid down into bone matrix by binding to the mineral phase, collagen or other matrix proteins.
There are two fractions of non-collagenous bone proteins—soluble and insoluble non-collagenous bone proteins. The fraction of insoluble non-collagenous bone proteins consist of bone growth factors—the growth factor ‘cocktail’, which is responsible for regulating bone formation. In the 1970's, M. Urist established procedures to isolate soluble and insoluble bone morphogenetic proteins from animal bones (for example, as described in “Bone morphogenesis in implants of insoluble bone gelatin.” Urist M R, Iwata H, Ceccoth P L, Doriman R L, Boyd S D, McDowell R M and Chien C. Proc Natl Acad Sci USA 1973:351 1-351 5, hereby incorporated by reference in its entirety (the Urist 1973 article). The method taught in Urist begins with crushed bone, and does not have a pre-washing step. A chloroform-methanol extraction is performed to remove blood, cells, and other debris from the bone. The method also includes a treatment step with lithium chloride, and treatment with HCl, CaCl.sub.2, and EDTA at 2.degree. C. The duration of the process is about 3.5 days, and the resulting ISBG contains BMP-2 only.
Bone morphogenetic activities were observed in implants of insoluble bone gelatin in several animal models described by Urist and other researchers including the present inventors. It has now been well accepted that bone gelatin can induce bone formation and control bone morphogenetic reaction.
It is believed that Gie et al. was first to describe the use of impaction bone allografting in revision surgery (for example, as described in “Contained morselized allograft in revision total hip arthroplasty.” Gie G A, Linder L, Ling R S, Simon J P, Slooff T J, Timperley A J Orthop Clin North Am 1993 24:717-725, hereby incorporated by reference in its entirety) and this technique has been used widely since then. Even with the improvement of techniques and materials used in this field, loosening still remains a big problem.